Photosynthetic responses of leafy veg to irradiance and CO2 concentration
Spinach, chard, and kale maximum Pn were 23.8, 20.3, and 18.2 μmol CO2·m−2·s−1 fixed, respectively, across varieties (400 ppm CO2). Spinach and kale had the highest and lowest light compensation points [LCPs (73 and 13 μmol·m−2·s−1, respectively)] across varieties.
The light saturation points (LSPs) for chard and kale were similar at 884–978 μmol·m−2·s−1, but for spinach, the LSP was higher at 1238 μmol·m−2·s−1. Dark respiration was lowest on kale and highest on spinach (−0.83 and −5.00 μmol CO2·m−2·s−1, respectively). The spinach CO2 compensation point (CCP) was lower (56 ppm) than the chard or kale CCP (64–65 ppm).
Among varieties, ‘Red Russian’ kale Pn saturated at the lowest CO2 concentration (858 ppm), and ‘Bright Lights’ chard saturated at the highest (1266 ppm; 300 μmol·m−2·s−1). Spinach Pn was more responsive to increasing irradiance than to CO2. Kale Pn was more responsive to increasing CO2 than to irradiance, and chard Pn was equally responsive to increasing CO2 or irradiance. Implications and limitations of this work when “upscaling” to whole-plant responses are discussed.
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